Commutator



0a. 21, 1930. Q MBo-R 1,778,820

C OMMUTATOR Filed July 11, 1928 2 Sheets-Sheet INVENTOR ATTORNEY Oct. 21, 1930. c, AALBORG 1,778,820

COMMUTATOR Filed July 11, 1928 2 Sheets-Sheet 2 ATTORNEY Patented Oct. 21, 1930 FATE? CHRISTIAN AALBORG, OF PITTSBURGH, ?ENNSYLVANIA, A$SIGNOR TO WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORAT ON OF PENNSYLVANIA COMMUTATOR Application file l July 11, 1928. Serial No. 291,?48.

My invention relates to commutators for dynamo-electric machines, and more particularly to the arrangement of parts in comtator cylinders for machines of high capacity.

In the construction of large commutators, it is necessary that every step be taken to construct a commutator in which the associated parts are combined to the best advantage in order to allow for stresses set up by the expansion of parts and by centrifugal action.

Since the commutator bars carry current, they are heated and expand, leaving the commutator cylinder with a rough surface and with the parts somewhat distorted. In large commutators, this expansion is considerable. The copper, having a greater coefficient of expansion and being run hotter than the asso ciated parts, will tend to stretch the bolts which hold the clamping rings.

It is an object of my invention to provide a commutator in which the parts are so combined that compensation for expansion of the commutator bars is provided and the initial stresses in the commutator cylinder are thereby maintained throughout any range of temperature that may develop.

It is another object of my invention to provide a commutator in which the commutator bars are given initial stresses upon assembling in order to prevent bulging in the middle by the actionof centrifugal force.

It is a further object of my invention to provide each commutator bar with a relieved edge-portion along the inner edge of the inwardly-projecting portion in order to prevent concentration of stresses in the V- recesses of the bars because of distortion of the V-ring.

A better understanding of my invention may be had by reference to the following description, taken with the accompanying drawing, in which Figure 1 is a longitudinal sectional view of a portion of a commutator cylinder in the form now preferred by me, and

Fig. 2 is a similar view of another commutator cylinder embodying some of the features of my invention.

In Fig. 1, is illustrated a spider 5 which is usually of cast steel and has a'plurality of holes 6 extending longitudinally near the periphery thereof and circumferentially spaced therearound. commutator bars 7 having radially-extending dovetail portions 8 and l-shaped recesses 9 and 10, are maintained on the surface of the spider by clamping rings 11 and 12, having inwardly-extending V-shaped portions which are wedged into the recesses 9 and 10 and are insulated therefrom by mica spacers, l3 and 14:. The V-rings 11 and 12 are maintained against the spider by a plurality of bolts 16 which are located in the holes 6 in the spider 5 and project from one end.

The portions of the bolts 16 within the holes 6 are surrounded by sleeves 17 which are preferably made of a non-expansive material, such as invar steel. The head 18 of each bolt 16 engages the corresponding end of the sleeve 17 to force its other end against a shoulder 19.

The clamping bolts 16 are alternately disposed around the commutator cylinder so,

that one half of the bolt heads 18 are located at one end and the other half are located at the other end.

Since copper has a greater coefficient of expansion than the material of the bolts and V-rings, there is considerable pressure created in a longitudinal direction against the V-rings. The V-rings being of different material and being run much cooler than the copper bars, they will not expand the same amount, and, consequently, the V-rings become distorted while the bolts stretch and bend inwardly. The spider is also at a lower temperature than the copper approximating that of the V-rings and, therefore, expands longitudinally a distance much less than that of the commutator bars.

The bolts are placed under considerable stress and, since they are placed in a nonexpansive sleeve, there will be no pressure acting against the heads 18 to move them outwardly from the holes. Consequently, the bolts are allowed free movement to the left, a distance equal to the expansion of thespider from the vertical axis 1 Y. In this manner, the total expansion of the parts may be considered as the summation of one half of the expansion of the spider and the expansion providedby a bolt of increased effective length.

The enormous intensity of the stresses which are set up by the longitudinal expansion may bev better appreciated by a mathematical discussion.

If it be assumed that copper bars expand 1.73 mils per inch under a 100 C. rise, and

steelex'pands only .55 mils perinch under 50 C. rise, the difference will be 1.18 mils per inch, which must be compensated ifor in the construction of the commutator. Hence,

a commutator bar 16' inches in active length.

will expand approximately 19 mils. As summing the bolts to be. 26 inches long, the

changein length per inch of length becomes .00077,which-multiplied by the modulusof elasticity for steel or 3 l0 gives a unit stress 22,000 lbs. per square inch set up in the bolts. By allowing movement of the bolts with expansion of the spider, and by the utilization of alternate bolts to get, in effect, boltswhich are substantially twice the length '01? the commutator cylinder, I

' manageto reducethe stress in the bolts to that of their initial, cool condition, and thereby obtainv a commutator cylinder. in which the stresses are kept in equilibrium,

regardless f of changes I in temperature. 7 -With commutator cylinders rotating at high speeds, there is a'tendency'tor the bars to bulgeout in the middle, thereby creating a rough surface, the amount ofbulging depending'upon the length of the commutator cylinder. Another feature of inyinvention prevents suchaction.

. It will'be note'dthatthe middle partot the outer surface of the spider has a larger diameter than its ends and that the tapering begins at the ends 21 and 21a of a cylindrical middle portion.

- In assembling the commutator bars, they are bent to -engagefthe spider surface, thus 4551 setting up initial 'stresse's'in the bars which are slightly greater than {any centrifugal stress-es which will be exerted at the middle clamp the barsdown over theends 21.=ancl- 21a. onthe surface 'of the spider 5;

The commutator bars are not only prevented from bulging at the middle but "are alsoigiven initial stresses at their ends, so

- th'a-t the entire surface of 'a commutator cylinder constructed in this manner ris pre vented 'fromgetting rough becauseof centrifugalforce. w

"surfaces of the recess.

. There also a, tendency for the V-rings to expand'circumferentially, and, if the inwardly; projecting portions -24: and 25 on the respective \l-rln-gs are maintained against the underedge of the spider'rim, a great deal of friction will result and the spider will thereby be prevented from expanding horizontally. I make allowance for .such expansion by undercutting the inner vfaces of the projecting portions 24e'and25 ot-the V-rings-and providing grooves inthe undercut faces-to receive felt rings 26 and 27,

respectively. V

In Fig.2, some of the-features described above'ar'e taken care o fina slightly different manner, and, at the same time, other features are shown..@ 7 r A sniderf31 is surrounded by a brass cylinder 32 on the outer surface 01 which are I disposed the copper commutator bars ,33 which are separated fromthe cylinder 32 by the usualmica insulation 34. V

r The ti-rings '35 and 36am maintained in the recessesfil and 38 of the commutator bars by bolts-39 which-jars insertedir'ithe ends of thecylinder-32. The bolts 39 are provided with sleeves 41 of invar steel'inorderto'increase their expansion length, giving them nearlytwice the expansionbf bolts utilized heretofore... w p Y The brass cylinder 32 preferably has its inneriperiphery fitted into a wedge-shaped groove 42 provided inthe outensuri ace or" the spider. The brass, being of-nearly thesame coeliicient of expansion, will expand radially nearly the same distance as the copper, and, in that way, serve to fill in algap which tends to iorm'between the spider surface andthe bottoms of i the copper bars but this' expane sion is not quite enough to keep the stresses uniform throughoutitheistructure- By reason of the wedge shaped groove 42, I provide meanswvhereby the clearance is required .to take place between the brass-and the spider element. The brass notonly expands radially, but expands longitudinally, and, therefore, the sloping surfaces 43 iands l ltend to creep up on tlie wedge walls of the groove since a resultant sliding force acts along the line of contact, and the brass ring is thereby kept against "tl1 bottom surfaces-of the copper commutator bars It will be understood that various modifications may be made in the arrangement of parts, and it is intended to cover herein such modifications as fall within the spirit and scope of my invention as defined in the appended claims.

I claim as my invention:

1. A commutator comprising a cylindrical spider, commutator bars disposed on said spider and insulated therefrom, clamping rings engaging the ends of said bars, bolts for forcing said rings against the ends of said bars, and sleeves oi non-enpansible material surrounding portions of said bolts and abutting against a portion of said spider.

2. A commutator for a dynarnoelectric machine comprising a cylindrical spider having longitu(finally-extending holes, commutat-or bars disposed on said spider, clamping rings, and means for clamping said rings comprising bolts located in said holes and projecting the et'rom at one end, sleeves oi non-expansible material surrounding said bolts Within said holes.

3. A commutator tor a dynamo-electric machine comprising a cylindrical spider hav ing longitudinally-entending holes, commutator bars disposed on said spider, clamping rings adapted to engage the ends of said bar-s, means for clamping each of said rings in end engagement with said bars comprising bolts sed in said holes, each of said bolts being r than the distance between said clampl rin s, and sleeves cooperating With said bolts Where-by tl e stresses set up by expansion of said bars is transferred to members having substantially twice the active length of said commutator bars.

i. in a commutator, the combination of a cylindrical spider having a plurality of holes extending therethrough, commutator segments, if-rings disposed at the respective ends said segments, means for clamping said ings to said segments in such manner as to crease the strain on said bolts by axial eX- -L.nsion of said segments, said means comorising bolts extending through said holes, sleeves of material dissimilar from said bo s surrounding the portions of the bolts .LL Wl'tllll said holes.

the combination of a commutator bars disposed 'ings, and means for clamp- -rin 's to l i saie said bars comprising disposed i? so d holes, adjacent bolts entenoing in opposit directions and the portions of the bolts lying Within said holes being surrounded by rleeves of nonexpansible material, th reby increasing the effective lengths of said bolts to decrease the strain at any section by axial expansion of said bars.

6. in a commutator, the combination of a pider having iongitudinally-extending holes herethrough, commutator bars surrounding said spider nd insu -ted theretr m, clamping rings en; ging the ends or said bars, and

- ior cramping one of said rin 1 comlocated in some of said holes,

amp-ir anothe of said ri 11 holes, su rounding the 1 vvitn'n said holes.

comm tor .wv W "A aaing a iveri en d recess, the outer sur- 1 T inclined at n an poinons conforn to eac bars being bent do" 0 d having V-SllZLPGCl ions, if-rings adapted said recesses, means for clamping a to cause the latter to hold the v the surface or said spider, the

bottom edges said bars having relieved portions spaced fronrthe spider at the ends of the bars. whereby, ipon distortion or said rings, the ends of the bars may deflect an amount corresponding to the distortion of the rings.

10. In a commutator member, the combina- J. 1

prising a cylindrical spider having a grooved surface, a brass cylinder surrounding said spider and adapted to fit said grooved surface and engage inclined surfaces near the outer ends thereof, commutator bars disposed on said cylinder, J-rings engaging the ends of said bars, and means for clamping said rings, said commutator bars being maintained in contact with said brass cylinder at any commutator temperature by circumferential eX- pansion and radial movement due to longiudinal expansion acting against said inclined surfaces.

12. A commutator cylinder comprising copper bars having \I-grooves in their ends, V- rings engaging said grooves, a supporting spinder 101' said commutator bars and if-rings, bolts for securing said V-rings to said sup porting spider, and spacing means having a very low coefiicient of expansion, as compared to the bolts, interposed between the ends of He bolts so as to increase the bolt length.

13. The invention, as defined in claim 1.2, characterized by the fact that alternate bolts ext nd to opposite ii-rings.

14. The invention, as defined in claim 12, characterized by the fact that alternate bolts extend to opposite V- ings and the inner boltheads ofthebolts Which extend to one V-ring 17; extend into close proximity to the other V- ring, whereby substantially the maximum practicable length of bolt is obtained.

In testimony whereof, I have hereunto subscribed my name this 5th day of July, 1928.

CHRISTIAN AALBORG. 

